ui: overhaul files, kanban, calendar, settings, chat modules

- FileBrowser: modernize breadcrumbs, toolbar, list/grid items, empty states
- KanbanColumn: remove fixed height, border-based styling, compact header
- KanbanCard: cleaner border styling, smaller tags, compact footer
- Calendar: compact nav bar, border grid, today circle indicator, day view empty state
- DocumentViewer: remove bg-night rounded-[32px], border-b header pattern
- Settings tags: inline border/rounded-xl cards, icon action buttons
- Chat: create +layout.svelte with PageHeader, overhaul sidebar and main area
- Chat i18n: add nav_chat, chat_title, chat_subtitle keys (en + et)

svelte-check: 0 errors, vitest: 112/112 passed

messages/en.json

@@ -254,6 +254,9 @@
 	"entity_invite": "invite",
 	"entity_event": "event",
 	"nav_events": "Events",
+	"nav_chat": "Chat",
+	"chat_title": "Chat",
+	"chat_subtitle": "Team messaging and communication",
 	"events_title": "Events",
 	"events_subtitle": "Organize and manage your events",
 	"events_new": "New Event",